WO2018178747A1

WO2018178747A1 - A spherical solar tracker

Info

Publication number: WO2018178747A1
Application number: PCT/IB2017/051875
Authority: WO
Inventors: Xavier Jean Germain THIBERT
Original assignee: Xtuas Oü
Priority date: 2017-03-31
Filing date: 2017-03-31
Publication date: 2018-10-04

Abstract

A spherical solar tracker (1) for orienting a solar energy device toward the Sun, said tracker comprises a top connector (3), adapted to be mechanically connected to said solar energy device, a base connector (2), adapted to be mechanically connected to the ground or a building, connected to each other through a set of three branch assemblies (6a, 6b, 6c) comprising each a rigid leg (7a, 7b, 7c) connected to a corresponding rail (8a, 8b, 8c) with a chariot assembly (9a, 9b, 9c). Each chariot assembly forms a cylindrical joint (11a, 11b, 11c) on said rail. Each leg is attached to chariot through revolute joint (12a, 12b, 12c). Another end of each leg is attached to the top connector through another revolute joint (13a, 13b, 13c).

Description

A SPHERICAL SOLAR TRACKER

TECHNICAL FIELD

The invention is a solar tracker for orienting solar energy devices (like solar photovoltaic panels) toward the Sun. A solar tracker increases the harvested solar energy by keeping a solar panel perpendicular to the Sun radiation.

BACKGROUND ART

A solar tracker is a device that orients a payload toward the Sun. Payloads are usually solar panels, parabolic troughs, fresnel reflectors, mirrors or lenses.

Known are single axis trackers, having one degree of freedom that acts as an axis of rotation. The axis of rotation of single axis trackers is typically aligned along a true North meridian. It is possible to align them in any cardinal direction with advanced tracking algorithms. There are several common implementations of single axis trackers. These include horizontal single axis trackers (HSAT), horizontal single axis tracker with tilted modules (HTSAT), vertical single axis trackers (VSAT), tilted single axis trackers (TSAT) and polar aligned single axis trackers (PSAT). The orientation of the module with respect to the tracker axis is important.

Also known are dual axis trackers two degrees of freedom that act as axes of rotation. These axes are typically normal to one another. The axis that is fixed with respect to the ground can be considered a primary axis. The axis that is referenced to the primary axis can be considered a secondary axis. There are several common implementations of dual axis trackers. They are classified by the orientation of their primary axes with respect to the ground. Two common implementations are tip-tilt dual axis trackers (TTDAT) and azimuth-altitude dual axis trackers (AADAT). The orientation of the module with respect to the tracker axis is important when modeling performance. Dual axis trackers typically have modules oriented parallel to the secondary axis of rotation. Dual axis trackers allow for optimum solar energy levels due to their ability to follow the Sun vertically and horizontally. No matter where the Sun is in the sky, dual axis trackers are able to angle themselves to be in direct contact with the Sun.

Horizontal single axis trackers are typically used for large distributed generation projects and utility scale projects. The combination of energy improvement and lower product cost and lower installation complexity results in compelling economics in large deployments. In addition the strong afternoon performance is particularly desirable for large grid-tied photovoltaic systems so that production will match the peak demand time. Horizontal single axis trackers also add a substantial amount of productivity during the spring and summer seasons when the Sun is high in the sky. The inherent robustness of their supporting structure and the simplicity of the mechanism also result in high reliability which keeps maintenance costs low. Since the panels are horizontal, they can be compactly placed on the axle tube without danger of self-shading and are also readily accessible for cleaning.

A vertical axis tracker pivots only about a vertical axle, with the panels either vertical, at a fixed, adjustable, or tracked elevation angle. Such trackers with fixed or (seasonally) adjustable angles are suitable for high latitudes, where the apparent solar path is not especially high, but which leads to long days in summer, with the Sun traveling through a long arc.

Dual axis trackers are typically used in smaller residential installations and locations with very high government feed in tariffs.

There is considerable argument within the industry whether the small difference in yearly collection between single and dual-axis trackers makes the added complexity of a two-axis tracker worthwhile. A recent review of actual production statistics from southern Ontario suggested the difference was about 4% in total, which was far less than the added costs of the dual-axis systems. This compares unfavorably with the 24-32% improvement between a fixed-array and single-axis tracker.

What is needed, therefore, is simpler solar tracker device that has the least amount of elements, is easy to manufacture and is thus more cost effective compared to known alternatives.

DISCLOSURE OF INVENTION

These and other goals of the invention are achieved by a spherical solar tracker for orienting a solar energy device toward the Sun, said tracker comprises a top connector, adapted to be mechanically connected to said solar energy device, a base connector, adapted to be mechanically connected to the ground or a building, said top connector and said base connector mechanically connected to each other through a set of three branch assemblies, wherein each branch assembly comprises a rigid leg, connected to a corresponding rail with a chariot assembly, wherein each chariot assembly is attached to said corresponding rail by the means of a cylindrical joint, movable along and rotatable around said rail, and a revolute joint attached to said rigid leg, wherein each said leg is connected to the top connector with a second revolute joint and said rails are rigidly fixed to each other and to a base connector, and radially extending from a common center.

BRIEF DESCRIPTION OF DRAWINGS

Embodiments of the present invention will now be described, by way of example, with reference to the accompanying drawings in which:

Fig 1 is a top side view of a spherical solar tracker together with a solar panel;

Fig 2 is a top side view of a spherical solar tracker;

Fig 3 is a side view of the spherical solar tracker;

Fig 4 shows one exemplary synoptic position of the mechanism;

Fig 5 shows another exemplary synoptic position of the mechanism;

Fig 6 shows a spherical solar tracker together with a control unit;

Fig7a is a top view and Fig 7b is a side view of the cone of maximum orientation; and

Fig 8 is a top side view of an assembly with a solar panel comprising two devices stacked together.

EXAMPLES FOR CARRYING OUT THE INVENTION

As shown in Fig 1, the spherical solar tracker 1 for orienting a solar energy device 4 toward the Sun comprises a base connector 2 and a top connector 3. The top connector 3 is adapted to be mechanically connected to and for carrying a solar energy device 4 while the base connector is adapted to be mechanically connected to an appropriate supporting structure such as the ground or a wall or a roof of a building, or any other suitable structure. The top connector 3 and base connector 2 are mechanically connected to each other through a set of three branch assemblies 6a, 6b and 6c (see in details also Figs 2 to 5). Each branch assembly comprises a rigid leg 7a, 7b and 7c, connected to a corresponding rail 8a, 8b and 8c with a chariot assembly 9a, 9b and 9c. Each chariot assembly 9a, 9b and 9c comprises a cylindrical joint 11a, l ib and 11c, movable along and rotatable around the corresponding rail. Each chariot assembly 9a, 9b and 9c also comprises a revolute joint 12a, 12b and 12c attached to the one end of said leg. In its second end the leg is connected to the top connector 3 with a second revolute joint 13a, 13b and 13c. The three branches are preferably evenly distributed on a circle whose center is the center of the base connector. Each rail is rigidly mounted on top of and along the radius of the base connector. The three branches are evenly distributed on a circle whose center is the center of the base connector 2 and are aligned accordingly to the connections of the three branches and the top connector 3. The device is a parallel mechanism with an innovative arrangement of one cylindrical joint and two revolute joints known as a 3- CRR parallel manipulator.

Each chariot assembly and rail form a linear actuator with two degrees of freedom that may be actuated manually or with three motors 14a, 14b and 14c attached to each respective rail 8a, 8b and 8c on the base connector. Each rail may take the form of a threaded rod with the corresponding inner thread formed in said chariot.

The angular orientation and vertical position of the top connector related to the base connector is determined by the combination of the respective positions of the three chariots along their respective rails (see Fig 5 and Fig 6). The appropriate azimuth and elevation of the position is calculated from astronomical data, sensor data or external data or commands sent to the device. An algorithm installed in the computing unit attached to the device transforms the altitude and azimuth of the requested position to the distances between extremities of each rail to its respective chariot. The same unit provides the means to control the motors 14a, 14b and 14c.

For a fully automated solar tracker, the device uses a control unit 17 shown in Fig 6 comprising means for receiving environment sensor data 18, means for storing sun astronomical data 19, means for receiving external data and commands 20, computing means for calculating spherical angle based on input data and commands 21, computing means 22 for calculating the positions for each of the chariots on corresponding rails, means for driving 23 each of the motors 14a, 14b and 14c according to the best orientation between the base and top connectors in order to keep the solar panel perpendicular to the Sun radiation or closer to the perpendicular Sun radiation. The control unit and the motors can use energy harvested with the solar panel or from any other power source.

The device provides quick and precise manipulative capabilities to orientate a solar energy devices attached to the top connector with limitations in possible orientations according to the predetermined cone of maximum orientation (Figs 7a and 7b). The described 3-CRR mechanism is limited in the range of orientations that can be reached between the base and top connectors when modifying the positions of each chariot along its respective rail. The bottom of the cone corresponds to the intersection of the three rails near the center of the bottom connector. The upper shape of the cone of maximum orientation shows the outer maximum azimuth and elevation that can be reached.

The cone of maximum orientation can be extended by superposing two devices 1 and , the second device 1 ' having its base connector attached to the top connector of the first device 1 (see Fig 8). When the second device is positioned with a 60 degrees offset from the first device around the vertical axis, the cone of maximum orientation is equal to a half-sphere.

Claims

1. A spherical solar tracker (1) for orienting a solar energy device toward the Sun, said tracker comprises a top connector (3), adapted to be mechanically connected to said solar energy device, a base connector (2), adapted to be mechanically connected to the ground or a building, said top connector and said base connector mechanically connected to each other through a set of three branch assemblies (6a, 6b, 6c), wherein each branch assembly comprises a rigid leg (7a, 7b, 7c), connected to a corresponding rail (8a, 8b, 8c) with a chariot assembly (9a, 9b, 9c), wherein each chariot assembly (9a, 9b, 9c) is attached to said corresponding rail (8a, 8b, 8c) by the means of a cylindrical joint (11a, l ib, 11c), movable along and rotating around said rail and a revolute joint (12a, 12b, 12c) attached to said rigid leg, wherein each said leg is connected to the top connector (3) with a second revolute joint (13a, 13b and 13c) and said rails (8a, 8b, 8c) are rigidly fixed to each other and to a base connector, said rails radially extending from a common center.

2. A solar tracker as in claim 1, wherein said rails are radially extending from said common center at 120 degree angle.

3. A solar tracker as in claims 1 to 2, wherein each of said second revolute joints are attached to said top connector (3) at each of the vertexes of an equilateral triangle.

4. A solar tracker as in claims 1 to 3, wherein all said rigid legs have the same length.

5. A solar tracker as in claims 1 to 4, wherein all said rails have the same length.

6. A solar tracker as in claims 1 to 5, wherein each of said rails is a threaded rod and each of said chariots has an inner thread matched for said threaded rod to form a cylindrical joint.

7. A solar tracker as in claim 6, wherein each threaded rod is equipped with a motor at its one end for rotating said threaded rod.

8. A solar tracker as in claims 1 to 5, wherein each chariot is equipped with a linear motor for moving each of said chariots on each of said rails.

9. A solar tracker as in claims 7 to 8, comprising a control unit for driving said motors.